DITA XML Schema Readme

The DITA XML Schema has the following directory structure within the standard DITA package:

 schema
   java

There are a number of tools available to create and validate DITA XML Schemas. Here is a small list:

• WebSphere^(R) Studio Advanced Developer 5.1
• jEdit 4.1
• Xerces 2.4.X

You can invoke Xerces XML document validation using SAX or DOM via the command-line

 java sax.Counter -v -s [xmlDocument]
 java dom.Counter -v -s [xmlDocument]

The DITA XML Schema architecture attempts to follow the naming convention established in the current DITA DTD architecture. Each element has there own named content model, i.e., topic.class for the topic element. Attributes that have an enumerated list of values in the DTD has their own class too, i.e. importance-att.class for the attribute important.

• All the elements in the base topic module are global. This will allow any element to be specialized.
• All the attributes are local to the element's content model, except for the class attribute.
• All the parametric entities in the DTD are named element groups with the same name as the DTD,i.e., basic.ph and ph.cnt.
• All elements in specialized schema module are declared globally as abstracted elements, except for the root element. The specialized element must also be declared locally in the derived content models.

Here are some simple steps that will make specialization easier:

1. Create a new XML Schema document.
   • Copy the contents of the parent specialization into the new *.xsd file.
   • Add an include statement for the *.mod in the XML Schema document.

     <xs:include schemaLocation="mySpec.mod" />

2. Create a new XML Schema module.
   • Create a new global element.
     • Add the substitutionGroup attribute. Its value is the parent specialization element.
     • If the new element in not a root element, set the abstract attribute to true.
   • Create a new content model for the root element. For most elements the following template will do.

         <xs:complexType name="myElement.class" mixed="" >
           <xs:complexContent>
               <xs:restriction base="myParentElement.class">
     
               </xs:restriction>
            </xs:complexContent>
         </xs:complexType>

   • Copy the content of the parent element's content model, every thing between the elements <xs:choice>, <xs:sequence>, or <xs:all>, into the new element's content model. For example:

         <xs:choice minOccurs="0" maxOccurs="unbounded">
     
         </xs:choice>

   • Local element substitution
     • Modify the class attribute default value
     • Optional - modify element content model

The DITA XML Schema is an experiment to determine the merits of XML Schema to create and maintain specialized content. The XML schemas should be considered as "work in progress". Any document that is validated using the current DTDs in the DITA package will be valid using the XML schemas.

The schemas can be validated using Xerces, IBM's Schema Quality Checker from alphaWorks^(R), or most XML editors.

Validating the XML schemas using Xerces or IBM's SQC will generate some errors related to particle restriction rules.

[Error] task.mod:157:37: rcase-Recurse.2: There is not a complete functional mapping between the particles.
[Error] task.mod:157:37: derivation-ok-restriction.5.3.2: Error for type 'step.class'.  The particle of the type is not a valid restriction of the particle of the base.

[Error] task.mod:96:41: rcase-MapAndSum.1: There is not a complete functional mapping between the particles.
[Error] task.mod:96:41: derivation-ok-restriction.5.3.2: Error for type 'taskbody.class'.  The particle of the type is not a valid restriction of the particle of the base. 

These errors will not affect document validation. One of the requirements for XML Schema 1.1 is to relax the particle restriction rules.